<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>函数的参数</title>
    <script>
        function fun(a,b){
            console.log(a+b);
        }
        fun(1,2);   //3
        fun(5);    //NaN
        fun(4,5,6);  //9
    </script>
</head>
<body>

</body>
</html>